1. Field of the Invention
The present invention relates to a regenerative braking apparatus for a battery operated vehicle, which is ideally used for control at the time of regenerative braking of a propulsion motor of a battery operated forklift to reduce the motion that an inner wheel is moved by a truck locus at the time of regeneration close to the steering angle for inside wheel stop turning.
2. Description of the Related Art
Heretofore, forklifts equipped with a battery as a power source and propelled by a motor supplied from the battery, as the drive source, are known.
FIG. 3 is a schematic diagram illustrating a three wheeled battery operated forklift with two propulsion motors to which is applied a conventional regenerative braking apparatus. In FIG. 3, numeral 1 denotes a battery, 2 an accelerator, 3 a propulsion motor control unit, 4a and 4b propulsion motors, 5 transmission units, 6 rotation sensors for detecting the rotational speed of the propulsion motors, 7a an outer wheel (when turning) of two front wheels of the forklift, 7b an inner wheel (when turning) of the two front wheels of the forklift, and 8 a steering angle sensor.
The steering angle sensor 8 is a sensor for detecting a steering angle .theta. as shown in FIG. 4, subtended between an axis X1 common with the outer wheel 7a and inner wheel 7b of the forklift 9, and an axis X2 of a rear wheel 10.
With this forklift 9, the steering angle .theta. subtended between the axis X1 common with the outer wheel 7a and inner wheel 7b, and the axis X2 of the rear wheel 10, is detected by the steering angle sensor 8. Then, as seen in FIG. 3, by means of the propulsion motor control unit 3, regeneration circuits for each of the outer wheel 7a and the inner wheel 7b are switched corresponding to the steering angle .theta..
By respectively controlling the propulsion motor 4a of the outer wheel 7a and the propulsion motor 4b of the inner wheel 7b in this way, then in the case where the intersection point of the axis X1 and the axis X2 is outside of the forklift 9, the propulsion motor 4a and the propulsion motor 4b are made to act together as regenerative brakes in the forward direction or the reverse direction, to thereby effect regenerative braking. Furthermore, in the case of turning with the intersection point of the axis X1 and the axis X2 inside of the forklift 9 (between the outer wheel 7a and the inner wheel 7b), then the propulsion motor 4a can be made to act as a regenerative brake in the forward direction, and the propulsion motor 4b as a regenerative brake in the reverse direction, or the propulsion motor 4a can be made to act as a regenerative brake in the reverse direction and the propulsion motor 4b as a regenerative brake in the forward direction.
With the conventional forklift described above, in the case where the steering angle .theta. is small, there is no particular concern of a problem occurring.
However, in the case where the rear wheel 10 is turned by a large amount, as shown in FIG. 5, the intersection point C of the axis X1 and the axis X2 becomes very close to the inner wheel 7b, and there is the situation where the steering angle .theta. is substantially the same as that for inner wheel stop turning. In this case there is the problem that regenerative braking cannot be properly applied to the propulsion motor of the inner wheel 7b, since the propulsion motor is rotated by the action of the outer wheel 7a, as the motion that the inner wheel 7b is moved by a truck locus.
In the case where the propulsion motor 4b of FIG. 3 is rotated by external action, the situation arises where the regenerative direction of the inner wheel 7b differs from the drive direction, so that an optimum circuit current does not flow in the propulsion motor 4b, and sufficient regenerative braking is not obtained.
This phenomena appears noticeably at the time of regeneration close to the inner wheel stop turning.
The present invention takes into consideration the above situation, with the object of providing a regenerative braking apparatus for a battery operated vehicle, which can effect control of regeneration with good efficiency at the time of turning, without the concern of the motion that an inside wheel propulsion motor is rotated by a truck locus, even when close to the steering angle for inner wheel stop turning.